If the probability that two strangers meet and fall in love in the vast sea of people is very small, how likely are the two stars in the vast universe to meet and merge?
At the just-concluded American Astronomical Society, Larry Molnar, an astronomy professor from Calvin College in the United States, released an exciting news: around March 2022, two low-quality stars in the Milky Way will merge.
As soon as the news was published, it aroused strong public interest. After all, not many humans have the opportunity to witness the merger of two stars in their lifetime.
Where are these two stars? How far is it from us? What force created this shocking collision? How many years will the merger of these two behemoths last? Dinosaurs just witnessed the encounter between a comet and a planet, and they were almost wiped out. Then, five years later, when these two stars finally collided, what wonders will we witness? What impact will this collision have on our home planet Earth?
Let’s explore it in detail and do some homework in advance for this cosmic "encounter".
1800 light years away: long gestation and rapid merger
As you probably know, in our galaxy, there is a constellation Cygnus, and these two merging stars are in Cygnus. They form a star binary system called KIC 9832227, which is about 1800 light years away from us.
As early as January 2015, Professor molnar and others published relevant contents at the American Astronomical Society, and identified KIC 9832227 as a binary system that is likely to be merged.
They analyzed the data of this system from 1999 to 2014, and found that its cycle was continuously decreasing, and the decreasing trend was very similar to that before the outbreak of Scorpio V1309, and there was also a star merger event in Scorpio V1309. In 2015-2016, Professor molnar and others used further observation data to verify their previous inference, and finally confirmed that the system would be merged one day.
However, there are as many as 200 billion to 400 billion stars in the Milky Way, and nearly one third of them are located in binary or multi-star systems. It seems not uncommon for two stars in a binary system to merge.
Is this really the case? This requires us to understand the classification of binary systems first.
We can easily understand the "binary star system", that is, a system consists of two celestial bodies; These two celestial bodies can be ordinary stars or dense celestial bodies with high density, such as neutron stars or black holes.
In astronomy, we can classify binary systems according to many standards, one of which is the distance between two celestial bodies. For a "wide binary", the two celestial bodies are far apart and have little interaction. Two celestial bodies that are close to each other are called "close binaries", and it is possible for them to influence each other or transmit matter. Among the numerous binary systems in the Milky Way, there are only about 40,000 pairs of close binary stars, which can be said to be very rare.
Some close binary stars are too "intimate" and even come into contact, so we call them "contact binary". In an extreme case, the passing binary stars are so "close" that the two celestial bodies share the same external gas envelope. Generally speaking, it takes millions or billions of years for them to reach the stage of sharing the cladding, and once they enter the stage of sharing the cladding, the two stars will merge quickly, taking only a few months or years. Compared with the long years before sharing the envelope, the process of merger is like a blink of an eye, which is like a couple who have been in love for a marathon and then got married quickly after proposing marriage.
The binary star system KIC 9832227 mentioned above is in the final stage of shared cladding. According to the existing theoretical estimation, the two stars will merge in about five years.
The merger of binary stars will bring us a bright new star.
According to the current spectral data analysis, the mass of the two stars to be merged does not exceed 0.4 solar mass, which belongs to the category of the least mass stars we know. They look red, and the surface temperature is about two or three thousand degrees Celsius. Judging from the current observation, the two stars have not merged, and their apparent brightness is about 12 magnitude, which has completely exceeded the lowest limit that human eyes can see (6 magnitude), so we can only observe with the help of telescopes. (Magnitude is a unit used to measure the brightness of celestial bodies. The higher the brightness of stars, the lower the magnitude value; Sirius, the brightest star we see at night, is about 0 magnitude. )
The whole process of merging these two stars will last for several weeks, which is like a flash compared with their life span of 10 billion years. In this "instant", their brightness will rapidly increase by 100,000 times, and the apparent brightness can reach about 2 stars. It will look as bright as Polaris, second only to the three brightest stars we see in the northern sky: Sirius (-1 magnitude), Vega (0 magnitude) and Antares (1 magnitude).
The result of this binary merger is that there is a new bright star in our night sky for the time being, and its color is still red, so we call it "red star". This new star will exist for at least 10 billion years, so why do we say that there is a new bright star "temporarily"? Because it will only be bright for a few weeks, and then it will fade away and hide in the darkness beyond our naked eyes in the vast universe.
The gravitational wave generated by the merger of two black holes in 2015 attracted the attention of the whole world. So, will the merger of these two stars also generate gravitational waves five years later?
The answer is yes. The merger of binary stars will also release gravitational waves with a certain energy, but it is very small and almost negligible. Almost all the energy is concentrated in the electromagnetic wave, so we can only rely on traditional telescopes for observation. The gravitational wave observatory (LIGO) in the United States should not be able to detect this merger.
The merger of binary stars has brought us a bright new star. Will it also bring some dangers?
If we want to predict the impact of this event on life on earth, we need to know how much energy is released during the merger process and whether it will have any impact on the earth’s atmosphere.
There is no doubt that the merger of two celestial bodies will produce explosions and release a lot of energy at the same time, but the amount of energy released depends on the density of the merged celestial bodies. For example, the merger of two neutron stars will produce a so-called gamma-ray burst, which will release a thousand times the energy of a supernova in about 1-2 seconds and produce extremely strong gamma rays-astronomers have discussed the impact of such bursts on the earth-if such celestial bodies erupt at us not too far away in or outside the Milky Way, life on earth will be doomed.
However, we don’t have to worry that the merger of these two small stars will have any impact on life on earth. Compared with the merger of other dense celestial bodies, the energy released by the merger of these two stars is very small, even less than the energy generated by some normal stars, not to mention the energy generated by them is mainly in the optical band. We’d better watch the beautiful red star with peace of mind.
Standing on the shoulder of Scorpio V1309, waiting for the new star.
Theoretically speaking, astronomers always believe that the merger of low-mass binary stars is one of the cradles for the birth of slightly larger stars. However, the real observation has only made some progress in recent decades, which is attributed to the development of some large-scale astronomical survey projects and the improvement of computer processing power. In the past decades, astronomers have observed similar explosions many times, such as M31 RV in the Large Magellanic Cloud in 1988, V4332 in Sagittarius in the Milky Way in 1994, and V838 system in Unicorn in 2002-these explosions may represent merger events, but we are not completely sure.
It was not until 2006 that humans really confirmed a binary merger. The supernova search project of the Lick Observatory found the explosion of M85 OT2006-1 in the M85 galaxy 60 million light years away from the Earth. Astronomers from the University of California, Berkeley and California Institute of Technology made a detailed analysis, and found that the explosion originated from the merger of two low-mass binary stars, which was different from other known nova explosions. However, due to the lack of monitoring information before the outbreak, we are very lack of understanding of the binary system before the merger. In this year, according to the observations, astronomers gave a name to the new star formed by the merger of binary stars: "luminous red novae".
The key to really help astronomers solve the mystery of "Red Nova" is hidden in Scorpio V1309. This system was first discovered by astronomy enthusiasts in China and Japan, and then they submitted the relevant information to the astronomical variable source monitoring organization of the International Astronomical Union. However, the detailed data of Scorpio V1309 comes from an optical gravitational lensing experiment (abbreviated as OGLE；; Optical gravity lens experiment). The project was officially started by astronomers of Warsaw University in Poland in 2001. The original intention was to monitor a large area of the sky, hoping to find celestial sources with changing brightness and discover the phenomenon of gravitational lens, so as to test some celestial bodies, such as black holes, which were originally thought to constitute dark matter. The location of Scorpio V1309 is just within the monitoring sky area of OGLE, so astronomers have obtained a large number of long-term observation data before and after the outbreak. Subsequent data analysis not only confirmed that this is a "red nova" system (a system after the merger of two stars), but also provided us with more important information, that is, how this binary system evolved with time before the merger.
It is on the basis of observation data and modeling before the merger of Scorpio V1309 system that Professor molnar and others judged the system evolution of KIC 9832227, and predicted that the "close contact" between the two stars and the final merger would take place between September 2021 and September 2022.
What are you waiting for? Go and put up a countdown card for the upcoming red star!
The video was produced by China, a popular science student, and was authorized to be published in the column "Learning Science with Xiaobian" of CCTV. Please indicate the source for reprinting.
Production: Black Hole Visitor Team Gou Lijun Huang Yue
Producer: computer network information center
